Power conversion system with energy harvesting

ABSTRACT

The present invention relates to a power conversion apparatus or system configured to receive a high voltage alternating current (AC) signal at an input and to provide in dependence thereon a low voltage direct current (DC) signal from an output stage. The power conversion apparatus comprises a main path comprising a high voltage capacitor in series with the input. In an example, the capacitor comprises a portion of an electric field energy harvesting system.

CLAIM OF PRIORITY

This application is a Continuation-in-Part of Hurwitz et al. U.S.application Ser. No. 14/912,514, filed on Feb. 17, 2016, whichapplication is a U.S. National Stage Filing under 35 U.S.C. § 371 ofInternational Patent Application Ser. No. PCT/GB2014/000328, filed Aug.22, 2014, and published on Feb. 26, 2015, as WO 2015/025121 A2, andwhich claims the benefit of priority of GB Application Ser. No.13150610.0, filed Aug. 22, 2013, each of which is incorporated herein byreference in its entirety.

TECHNICAL FIELD

The present invention relates to power conversion apparatus which isconfigured to receive an alternating current signal at an input and toprovide in dependence thereon a direct current signal from an outputstage. The present invention also relates to a power conversionarrangement comprising plural such power conversion apparatus.

BACKGROUND

Electronic apparatus is often powered from a mains electricity supply.Such electronic apparatus comprises power conversion apparatus which isoperative to convert a high voltage alternating current (AC) supply to alow voltage direct current (DC) supply. Power conversion apparatus canbe considered to belong to one of two different classes depending onwhether or not the power conversion apparatus comprises a transformer.Transformers provide for isolation and relatively loss free voltagelevel conversion, amongst other things, but on the other hand they aretypically large, heavy and expensive. Transformerless power conversionapparatus are comparatively inexpensive and small but are limited to lowpower applications and typically to less than 40 mW of direct currentoutput power. At present transformerless power conversion apparatus areused mainly in AC powered applications which are operative on the mainsside, such as in electricity meters, residual current detectors, homecontrol and monitoring, PIR controlled exterior lights and fire alarms.

Transformerless power conversion apparatus can be considered to belongto one of two classes, namely resistive transformerless power conversionapparatus and capacitive transformerless power conversion apparatus.Resistive transformerless power conversion apparatus are normallywasteful of power and therefore limited to few low power applications.Capacitive transformerless power conversion apparatus are less wastefulof power than resistive transformerless power conversion apparatus butyet may waste more than ten to twenty times the output power.

A simple representation of capacitive transformerless power conversionapparatus is shown in FIG. 1. The power conversion apparatus 10comprises a live connection 12 and a neutral connection 14 which areconnected respectively to the live and neutral conductors of a mainselectricity supply, such as a 240 V AC electricity supply. A firstcapacitor 16 and a resistor 18 are in series with the live connection.The first capacitor 16 is an X type capacitor which is designed toprovide for safety at mains voltage levels. The resistor 18 is presentto limit the inrush current to the first capacitor 16 if the powerconversion apparatus is connected to the mains at a point in the mainscycle other than the zero crossing or in the event of a mains surge. Thepower conversion apparatus 10 further comprises a diode 20 in serieswith the first capacitor 16 and the resistor 18 which is oriented suchthat its anode is electrically connected to the resistor 18. The powerconversion apparatus 10 also comprises a Zener diode 22 and a holdingcapacitor 24. The cathode of the Zener diode 22 is electricallyconnected between the resistor 18 and the diode 20 and the anode of theZener diode 22 is electrically connected to the neutral connection 14.The holding capacitor 24 is electrically connected between the cathodeof the diode 20 and the neutral connection. The power conversionapparatus 10 yet further comprises a positive voltage output connection26 at the diode 20 side of the holding capacitor 24 and a low voltageoutput connection 28 at the neutral side of the holding capacitor 24.The positive and low voltage output connections 26, 28 constitute theoutput from the power conversion apparatus 10. The breakdown voltage ofthe Zener diode 22 minus the voltage drop across the diode 20 determinesthe voltage across the holding capacitor 24 and hence the output voltagefrom the power conversion apparatus 10.

The present inventors have appreciated that the Zener diode 22 in thepower conversion apparatus of FIG. 1 provides for consumption of thesame power irrespective of the power output from the power conversionapparatus. This is because the consumed power comprises power shunted bythe Zener that is not used by the load. The greatest power conversionefficiency is obtained when the power conversion apparatus is operatingunder full load conditions with there being a progressive reduction inpower conversion efficiency as the toad decreases. The present inventorshave also appreciated that the power conversion efficiency of the powerconversion apparatus is compromised by the power dissipated by theinrush current limiting resistor 18 and the voltage dropped across theZener diode 22 irrespective of load conditions. The power dissipated bythe resistor 18 is a function of the reactance of the first capacitor 16and the resistance of the resistor 18.

The present invention has been devised in the light of the abovementioned appreciations. It is therefore an object for the presentinvention to provide improved power conversion apparatus which isconfigured to receive a high voltage alternating current signal at aninput and to provide in dependence thereon a low voltage direct currentsignal from an output stage. It is a further object for the presentinvention to provide an improved power conversion arrangement comprisingplural such power conversion apparatus.

SUMMARY

According to a first aspect of the present invention there is providedpower conversion apparatus configured to receive a high voltagealternating current signal at an input and to provide in dependencethereon a low voltage direct current signal from an output stage, thepower conversion apparatus comprising: a main path comprising a highvoltage capacitor in series with the input; a first path operative tocarry current carried by the main path in at least one of a positivegoing part and a negative going part of the high voltage alternatingcurrent signal; a second path operative to carry current carried by themain path in a positive going part and a negative going part of the highvoltage alternating current signal; and first and second switches whichare operative to determine when a respective one of the first and secondpaths carries current, in which the output stage receives currentflowing in the first path and at least one of the first and secondswitches is operable in dependence on a control signal derived from thelow voltage direct current signal.

The power conversion apparatus is configured to receive a high voltagealternating current (AC) signal, such as a mains AC signal, at the inputand to provide in dependence thereon a low voltage direct current (DC)signal, such as an electronic circuit power supply, at the output stage.A peak voltage of the high voltage AC signal may be higher than avoltage of the low voltage DC signal. Depending on the configuration ofthe power conversion apparatus as described below, the first path may beoperative to carry current in a positive going part only of the highvoltage AC signal, in a negative going part only of the high voltage ACsignal or in positive and negative going parts of the high voltage ACsignal. The second path is operative to carry current in a positivegoing part and a negative going part of the high voltage AC signal. Thepower conversion apparatus may be configured such that the second pathis operative to limit a voltage level within the power conversionapparatus. The second path may therefore be operative to perform aclamping action. The first and second switches may be operativesubstantially out of phase and perhaps out of phase with each otherwhereby the first and second switches are not closed at the same time.

The power conversion apparatus may be configured such that the firstpath is in series with the output stage and the second path is inparallel with the output stage. The second path may provide forconduction between a high side of the power conversion apparatus and alow side of the power conversion apparatus. The high voltage capacitormay be in series with a high side of the input to the power conversionapparatus. The power conversion apparatus may thus be configureddepending on operation of the first and second switches, as describedfurther below, to provide a positive low voltage DC supply. The outputstage of the power conversion apparatus may therefore be referenced to alow side of the input to the power conversion apparatus, such as neutralwhere the power conversion apparatus receives a mains AC signal on livewith respect to neutral. According to an alternative approach the outputstage of the power conversion apparatus may be referenced to a low sideof the input to the power conversion apparatus, such as live where thepower conversion apparatus receives a mains AC signal on neutral withrespect to live. According to an alternative approach, the high voltagecapacitor may be in series with a low side of the input to the powerconversion apparatus whereby the power conversion apparatus isconfigured depending on operation of the first and second switches, asdescribed further below, to provide a negative low voltage DC supply.The output stage of the power conversion apparatus may therefore bereferenced to a high side of the input to the power conversionapparatus, such as live where the power conversion apparatus receives amains AC signal on live with respect to neutral. According to analternative approach, the output stage of the power conversion apparatusmay be referenced to a high side of the input to the power conversionapparatus, such as neutral where the power conversion apparatus receivesa mains AC signal on live with respect to live.

The first path may comprise the first switch. The first switch may be inseries between the input to and the output stage of the power conversionapparatus, such as in a high side of the power conversion apparatus. Thesecond path may comprise the second switch. The second switch may be inparallel with high and low sides of the input to the power conversionapparatus. At least one of the first and second switches may be operatedin dependence on a control signal at a frequency higher than a frequencyof the high voltage AC signal.

The output stage may be configured to be attached to a load. The loadmay thus, in use, receive DC power from the power conversion apparatus.The output stage may be configured such that it comprises a high sideoutput conductor and a low side output conductor. The power conversionapparatus may comprise a holding capacitor which is electrically coupledin parallel with the output stage, such as between the high side outputconductor and the low side output conductor. During operation of thepower conversion apparatus the holding capacitor may be charged bycurrent flowing in the first path and may therefore be operative as areservoir to accommodate power demand from a load connected to theoutput stage. In some forms of the power conversion apparatus which aredescribed below the holding capacitor may be of lower value than isrequired in known circuits and may, in certain applications, not berequired.

Each of the first and second paths may be operative to carry current inless than all of a positive going part or a negative going part within acycle of the high voltage AC signal. The first or second path maytherefore be operative to carry current in at least one portion and morepreferably plural portions of a positive going part or a negative goingpart. For example a path may be operative to carry current during aportion which constitutes 25% of a complete positive or negative goingpart and perhaps during a portion in which a rate of change of the highvoltage AC signal is greatest. Alternatively at least one the first andsecond paths and more specifically the second path may be operative tocarry current for at least one cycle and perhaps for plural cycles. Forexample where load demand is low and where the power conversionapparatus comprises a holding capacitor there may be no need tore-charge the holding capacitor over plural complete cycles of the highvoltage AC signal. At least one of the first and second paths and morespecifically the first path may not be operative to carry current everypositive going part or negative going part. For example and as describedfurther below, the second path may be operative to carry current on anintermittent basis when a clamping action is required. By way of anotherexample the first path may be operative to carry current on anintermittent basis when current is required in the output stage, such asfor maintaining a level of charge on the holding capacitor having regardto load demand.

Indeed the power conversion apparatus may be operative such that neitherof the first and second paths carries current during a portion of acycle of the high voltage AC signal to thereby hold a present state ofthe power conversion apparatus. More specifically at least one of: thesecond switch may open before the first switch closes; and the firstswitch may open before the second switch closes. Providing for neitherof the first and second paths carrying current during a portion of thecycle in such a fashion may prevent closure of the second switchdischarging the holding capacitor where a holding capacitor is comprisedin the power conversion apparatus.

On the other hand, the portion of the cycle when neither of the firstand second paths carries current may be of limited duration to limit theextent to which the voltage on the low voltage side of the high voltagecapacitor excurses towards the voltage on the high voltage side of thehigh voltage capacitor. In certain forms, the first and second switchesmay be closed at the same time momentarily whereby the high voltagecapacitor is loaded. Excursion of the voltage on the high voltagecapacitor may be addressed thereby.

Each of at least one of the first and second switches may comprise twocontacts and a control input, a change in voltage level at the controlinput being operative to change between conduction between the twocontacts and lack of conduction between the two contacts. The powerconversion apparatus may be configured such that the control signal isapplied to the control input of the switch. The switch may comprise atleast one active device having a control input. More specifically theswitch may comprise at least one transistor, such as a pair of MOSFETsin a back to back configuration. Alternatively the switch may comprise asingle MOSFET, the single MOSFET being formed by an appropriatesemiconductor process such that the MOSFET is capable of supporting thehighest voltages present in the power conversion apparatus. The powerconversion apparatus may therefore be constituted at least in part in aCMOS integrated circuit. The at least one transistor may be comprised ina well whose voltage bias may be altered during operation to handle anincreased voltage range. The power conversion apparatus may comprise aprotection device, such a MOSFET acting as a cascade, in series with theat least one transistor. The power conversion apparatus may comprise aprotection device, such as a parasitic diode to the substrate or well,in parallel with the at least one transistor. Such a switch normally hasa lower voltage drop, for example less than 100 mV, than the like of adiode or Zener diode based switch.

As specified above, at least one of the first and second switches isoperable in dependence on a control signal derived from the low voltageDC signal. The power conversion apparatus may therefore further comprisea switch control circuit which is operative to generate at least onecontrol signal in dependence on a determination made in respect of acondition of at least one signal in the power conversion apparatus. Theswitch control circuit may be configured to measure at least one of avoltage and a current in the power conversion apparatus. The switchcontrol circuit may be further configured to compare a measurement witha reference value and to generate a control signal in dependence on thecomparison. According to an approach the switch control circuit may beoperative to measure a voltage across the second switch. According toanother approach the switch control circuit may be operative to measurea voltage across the first switch. According to yet another approach theswitch control circuit may be operative to measure a direction of flowof current in the second path. According to another approach the switchcontrol circuit may be operative to measure a voltage across the input,e.g. between live and neutral, such as by way of a potential divider.Each of these approaches may allow for determination of characteristicsof the cycle of the high voltage AC signal such as in respect of whenthe cycle is in the positive going part or in the negative going part.The switch control circuit may be operative to determine when a switchis opened and closed. The switch control circuit may be configured tomeasure a voltage at the output stage, to compare the measured voltagewith a reference value and to determine at least one of a switching dutycycle and a switch state in dependence on the comparison. The comparisonmay involve hysteresis to improve stability or reduce switchingfrequencies with the trade-off of tipple. The switch control circuit maythus be operative to control the voltage at the output stage to adesired level and within a desired range of ripple. The power conversionapparatus may be configured such that the second switch is operable independence on a control signal derived from the low voltage DC currentsignal. Operation of the second switch in this fashion may provide theadvantage compared with the like of a Zener diode of improving uponefficiency when a load is drawing less than the maximum power availableat the output stage by allowing for control of the second switch inaccordance with load demand. The capability to control at least one ofthe first and second switches and knowledge of the phase of the highvoltage AC signal may allow for regulation of the low voltage DC signalto advantageous effect. For example control may be effected to elevatethe level of the low voltage DC signal to allow for a reduction in thesize of the holding capacitor. By way of further example, control may beeffected to elevate the level of the low voltage DC signal to takeaccount of a period when charge availability is minimal or zero, i.e. ina dead period, such as at or around a peak or a trough of the highvoltage AC signal. The level of the low voltage DC signal may beelevated for a relatively short period of time only whereby the elevatedlevel may be such that lifetime requirements for the power conversionapparatus are still met. An elevated low voltage DC signal may enablethe holding capacitor to continue to deliver power during a dead periodand such that the level of the low voltage DC signal does not drop toolow.

In a first embodiment the power conversion apparatus may be configuredin dependence on when the first switch is operative such that the firstpath carries current in one of positive and negative going parts only ofthe high voltage AC signal. More specifically the first path may carrycurrent in a positive going part only of positive and negative goingparts of the high voltage AC signal. In addition the power conversionapparatus may be configured in dependence on when the second switch isoperative such that the second path carries current in negative andpositive going parts of the high voltage AC signal. When the first pathcarries current in the positive going part only of the high voltage ACsignal, the power conversion apparatus may be configured such that thesecond path carries current in negative going parts of the high voltageAC signal. When the first switch is operative such that the first pathcarries current in a portion of one of positive and negative going partsonly, the power conversion apparatus may be configured such that thesecond path carries current in the one of the positive and negativegoing parts when the first path is not carrying current. When the firstpath carries current in a portion of the positive going part, the secondpath may, for example, carry current in another portion of the positivegoing part as well as in the negative going part.

In the first embodiment the power conversion apparatus may comprisesolely one switch in the first path, i.e. the first switch, and solelyone switch in the second path, i.e. the second switch. As specifiedabove, at least one of the first and second switches is operative independence on a control signal derived from the low voltage DC currentsignal. In a first form the first switch may comprise a diode. The firstswitch may therefore be operative in dependence on voltage levels at theanode and cathode of the diode and without dependence on the controlsignal. The diode may be disposed in the power conversion apparatus toconduct and thereby provide for the first path carrying current in atleast a portion of the positive going part of the high voltage ACsignal. The anode of the diode may be disposed closer to the highvoltage capacitor than the cathode of the diode. The second switch maycomprise two contacts and a control input and a change in voltage levelat the control input may be operative to change between conductionbetween the two contacts and lack of conduction between the twocontacts. Otherwise the second switch may be of a form and function asdescribed above. In a second form of the first embodiment each of thefirst and second switches may each comprise two contacts and a controlinput with a change in voltage level at the control input beingoperative to change between conduction between the two contacts and lackof conduction between the two contacts. Otherwise each of the first andsecond switches may be of a form and function as described above. Powerconversion apparatus in which the first and second switches are bothoperable in dependence on a control signal may provide for anappreciable reduction in the size of the high voltage capacitor onaccount of an improvement in the tolerance of the low voltage DC signaland a lower voltage drop over the first switch. A tolerance of, forexample, a few percent may be achieved compared with the known Zenerdiode and diode circuit for which a tolerance of more than 20% is oftenrequired.

The present inventors have appreciated that a further improvement inpower output and efficiency may be gained by using the positive goingpart and the negative going part of the high voltage AC signal ratherthan one of the positive and negative going parts. Therefore andaccording to a second embodiment the power conversion apparatus may beconfigured such that the first path carries current in both the positivegoing part and the negative going part. More specifically the powerconversion apparatus may comprise an intermediate energy storingcomponent and third, fourth and fifth switches which are each operablein dependence on a control signal derived from the low voltage directcurrent signal. Each of the third, fourth and fifth switches maycomprise two contacts and a control input with a change in voltage levelat the control input being operative to change between conductionbetween the two contacts and lack of conduction between the twocontacts. The intermediate energy storing component may comprise one ofan intermediate capacitor and an intermediate inductor. The intermediateenergy storing component may be disposed in series between the highvoltage capacitor and the output stage such as in the high side of thepower conversion apparatus.

The power conversion apparatus may be configured such that a third pathcomprising the intermediate energy storing component may carry currentduring a first portion of one of the positive and negative going partsof the high voltage AC signal. More specifically the intermediate energystoring component may store charge during the negative going part. Thethird switch may be connected at a first end to a first end of theintermediate energy storing component which is closer of first andsecond ends of the intermediate energy storing component to the outputstage and at a second end to a low side of the power conversionapparatus. Where the intermediate energy storing component is anintermediate capacitor, the fourth switch may be connected at a firstend to a second end of the intermediate capacitor and at a second end toa low side of the power conversion apparatus. Where the intermediateenergy storing component is an intermediate inductor, the fourth switchmay be connected at a first end to the second end of the intermediateinductor and at a second end to the output stage. The fifth switch maybe connected at a first end to the first end of the intermediate energystoring component and at a second end to the output stage. The fifthswitch may therefore be in series between the intermediate energystoring component and the output stage. Where the power conversionapparatus comprises a holding capacitor, an end of the holding capacitormay be connected to the second end of the fifth switch. The third pathmay carry current upon closing of the first and third switches wherebythe intermediate energy storing component stores energy received fromthe input. Thereafter the first and third switches may open and thefourth and fifth switches may close where the intermediate energystoring component is an intermediate capacitor or the third and fourthswitches may close where the intermediate energy storing component is anintermediate inductor whereby charge flows from the intermediate energystoring component to the output stage. Where the power conversionapparatus comprises a holding capacitor, charge may flow from theintermediate energy storing component to the holding capacitor. Thefirst, third, fourth and fifth switches may be operated such that theyall close and open at least once during one of the positive and negativegoing parts of the cycle. More specifically the first, third, fourth andfifth switches may be operated at a frequency at least 10 times, 100times, 1000 times, 10000 times, 100000 times or 1000000 times higherthan the frequency of the high voltage AC signal.

The power conversion apparatus may further comprise a sixth switch whichis connected at a first end to the second end of the intermediate energystoring component and at a second end to the output stage where theintermediate energy storing component is an intermediate capacitor.Where the intermediate energy storing component is an intermediateinductor the sixth switch is connected at a first end to a second end ofthe intermediate inductor and at a second end to a low side of the powerconversion apparatus. During the other of the positive and negativegoing parts, the first and fifth switches may close whereby theintermediate energy storing component stores energy received from theinput. Where the power conversion apparatus comprises a holdingcapacitor, the holding capacitor may also store charge. Thereafter thefirst and fifth switches may open and the third and sixth switches mayclose stage where the intermediate energy storing component is anintermediate capacitor or the fifth and sixth switches may close wherethe intermediate energy storing component is an intermediate inductorwhereby charge flows from the intermediate energy storing component tothe output stage. Where the power conversion apparatus comprises aholding capacitor, charge may flow from the intermediate energy storingcomponent to the holding capacitor. The first, third, fifth and sixthswitches may be operated such that they all close and open at least onceduring the other of the positive and negative going parts of the cycle.More specifically the first, third, fifth and sixth switches may beoperated at a frequency at least 10 times, 100 times, 1000 times, 1000times, 10000 times, 100000 times or 1000000 times higher than thefrequency of the high voltage AC signal. The efficiency of powerconversion apparatus depends on power dissipation in the input to thepower conversion apparatus, which is a function of the reactance of thehigh voltage capacitor and the resistance of the inrush resistor wheresuch is present, and the voltage dropped across the second switch. Areduction in the capacitive reactance and in the voltage drop in thesecond embodiment of the present invention may provide for a significantimprovement in efficiency. The power conversion apparatus may beconfigured such that the second switch is operative as described above,such as when there is no need to charge the holding capacitor or in deadperiods. In certain circumstances the second switch may be operative toclamp the high voltage capacitor while the intermediate energy storingcomponent is charging the holding capacitor.

Where the intermediate energy storing component is an intermediatecapacitor, the first and third to sixth switches and the intermediatecapacitor may constitute a first path arrangement. In certain forms, thepower conversion apparatus may comprise plural first path arrangements,such as two first path arrangements. The plural first path arrangementsmay be operative out of phase with each other. According to a firstapproach each of the plural first path arrangements may comprise adifferent holding capacitor. The power conversion apparatus maytherefore comprise plural first path arrangements with each first patharrangement comprising a holding capacitor. The power conversionapparatus may be configured such that each of the plural first patharrangements provides a different low voltage DC signal. For example thepower conversion apparatus may be configured such that one first pathprovides a positive low voltage DC signal and another second pathprovides a negative low voltage DC signal. According to a secondapproach each of the plural first path arrangements may comprise thesame holding capacitor. The plural first path arrangements may thereforebe operative to charge one holding capacitor.

Having plural such first path arrangements may provide for smoothertransfer of power to the holding capacitor. By appropriate phasedcontrol of one first path arrangement relative another first patharrangement significant change in the voltage level on the high voltagecapacitor side of the first path arrangements may be minimised.

Where the intermediate energy storing component is an intermediateinductor, the intermediate inductor and the first and third to sixthswitches may constitute a first path arrangement. In certain forms, thepower conversion apparatus may comprise plural first path arrangements,such as two first path arrangements. Each first path arrangement maycomprise a different intermediate inductor and different fourth andfifth switches at least of the first and third to sixth switches. Theplural first path arrangements may be operative out of phase with eachother. According to a first approach each of the plural first patharrangements may comprise a different holding capacitor. The powerconversion apparatus may therefore comprise plural first patharrangements with each first path arrangement comprising a holdingcapacitor. The power conversion apparatus may be configured such thateach of the plural first path arrangements provides a different lowvoltage DC signal. According to a second approach each of the pluralfirst path arrangements may comprise the same holding capacitor. Theplural first path arrangements may therefore be operative to charge oneholding capacitor. In one form, each of the plural first patharrangements may comprise a different intermediate inductor anddifferent fourth and fifth switches with the first, third and sixthswitches being common to the plural first path arrangements. In anotherform, each of the plural first path arrangements may comprise adifferent intermediate inductor and different first and third to sixthswitches. The number of first path arrangements may depend on the ratioof the voltage between the input side of the intermediate inductor andthe low side to the voltage at the output stage with the ratio having abearing on the ripple present at the input or output stage. Where theratio is greater increasing the number of first path arrangements mayreduce the ripple.

The power conversion apparatus may further comprise a DC-DC converterand more specifically a low voltage DC-DC converter. The DC-DC convertermay be electrically coupled to the output stage. The DC-DC converter maybe configured to provide plural low voltage DC supply signals. Where thepower conversion apparatus comprises a holding capacitor, the DC-DCconverter may be operative to allow for greater ripple at the outputfrom the power conversion apparatus whereby a holding capacitor of lowercapacitance may be used. Alternatively or in addition, the powerconversion apparatus may further comprise a switching converter. Theswitching converter may be electrically coupled to the output stage. Theswitching converter may be configured to provide for increased currentat reduced voltage from the power conversion apparatus.

The power conversion apparatus may be configured to determine acondition of the high voltage AC signal and to provide control data independence on the determined condition. More specifically the powerconversion apparatus may be configured to determine a fault condition,such as a brownout or sag (i.e. loss or reduction in amplitude of asingle phase). The power conversion apparatus may comprise a controldata output, which may be coupled to a load, and the control data may bemade available at the control data output. A load may therefore becontrolled in dependence on the control data, for example, to enter alow power consumption state. Alternatively or in addition the powerconversion apparatus may be configured to identify a portion of a cycleof the high voltage AC signal and to provide control data in dependencethereon. For example the power conversion apparatus may be configured toidentify a dead period of the cycle or a period of high rate of changeof the cycle. The control data may be configured accordingly such thatwhen it is provided to a load the load is operative to vary its powerdemand. The power demand may be varied to, for example, switch a relaycomprised in the load or transmit a packet from a transceiver comprisedin the load.

The power conversion apparatus may be configured to receive control datafrom a load and to control its operation in dependence on the receivedcontrol data. When a load is about to enter a low power state or isabout to draw an increased level of power the control data may beconfigured accordingly and such that the power conversion apparatus iscontrolled appropriately. For example and where the load is about toenter a low power state, the power conversion apparatus may be operativeto delay or skip releasing the high voltage capacitor from ground. Byway of another example and where the load is about to draw an increasedlevel of power, the power conversion apparatus may be operative toincrease the level of charge on the holding capacitor. The switching ofa relay or a Silicon Controlled Rectifier (SCR) normally requires amomentary increase in power. Furthermore the increased level of powercan often be determined in advance. Also a load normally knows that arelay or SCR is about to be switched. The power conversion apparatus maytherefore he operative to charge the holding capacitor by an amountcorresponding to the upcoming increase in power demand with the excesscharge on the holding capacitor being used shortly afterwards uponswitching of the relay or SCR. A relay or SCR is often switched aroundthe zero-crossing point of the high voltage AC signal. The zero-crossingpoint of the high voltage AC signal is also when the peak level ofcurrent is delivered from the high voltage capacitor of the powerconversion apparatus. The approach of increasing the level of charge onthe holding capacitor according to the present invention may thereforebe advantageous from the perspectives of load power requirement andpower delivery capability. The transmission of data by way of a wired orwireless medium often requires a momentary increase in power. The levelof power required for transmission is usually several times higher thanthe level of power required for reception or several orders of magnitudehigher than the level of power required for idling. The power conversionapparatus may therefore be operative to charge the holding capacitor byan amount corresponding to the upcoming increase in power demand withthe excess charge on the holding capacitor being used shortly afterwardsfor data transmission. Elevation of the charge on the holding capacitormay be used to advantageous effect where a communications circuitcomprised in the load is time aligned with a beacon that is aligned tothe zero-crossing point of the high voltage AC signal. The charge on theholding capacitor may be elevated for a short period of time on accountof an upcoming increase in power demand being momentary. Manyreliability criteria restrict operating voltage levels on a time relatedbasis whereby a momentary elevation in charge on the holding capacitorhas minimal adverse effect on reliability criteria. The present approachmay provide for a momentary increase in the level of power drawn fromthe power conversion apparatus at the cost of an increase in the levelof ripple present in the low voltage DC signal.

The power conversion apparatus may comprise a communications circuitwhich is operable to provide for at least one of transmission andreception of data by way of the input to the power conversion apparatus.Where the input to the power conversion apparatus is coupled to a mainssupply, the communications circuit may provide for at least one oftransmission of data to and receipt of data from the mains supply. Thecommunications circuit may be powered from the low voltage DC signal.The power conversion apparatus may be configured to selectively couplean output from or input to the communications circuit to a part of thepower conversion apparatus. More specifically the power conversionapparatus may be configured to selectively couple the output from orinput to the communications circuit to the low voltage side (or outputstage side) of the high voltage capacitor. The power conversionapparatus may comprise a communications switch, which is a switch ofcontrollable form as described elsewhere herein. The communicationsswitch may be connected at one end to the output from or input to thecommunications circuit and may be connected at another end to the partof the power generation apparatus, e.g. to the output stage side of thehigh voltage capacitor. The power conversion apparatus may be configuredsuch that the communications switch is closed when the first and secondswitches are open. The power conversion apparatus may be configured suchthat the communications circuit is operative to communicate around thezero-crossing point of the high voltage AC signal. The zero-crossingpoint is a period of maximal power transfer whereby the holdingcapacitor may readily recharge. Examples of appropriate communicationprotocols are X10 and lnsteon amongst others.

The power conversion apparatus may further comprise an inrush resistor.More specifically the inrush resistor may be disposed in series with theinput, such as in the high side of the input. The inrush resistor may beconstituted by a high wattage resistor and may serve to limit thecurrent when the power apparatus is plugged in or when it is subject toa surge event. Alternatively or in addition the power conversionapparatus may further comprise a Negative Temperature Coefficientresistor or a thermistor in series to minimise the inrush current butsuch that the current is not limited when the power conversion apparatusis operating and warm. Alternatively or in addition the power conversionapparatus may further comprise a discharge resistor which is connectedacross the high voltage capacitor. Alternatively or in addition thepower conversion apparatus may further comprise a varistor, such a metaloxide varistor, which is connected between the high and low sides of thepower conversion apparatus with one end of the varistor being connectedon the output stage side of the high voltage capacitor whereby thevaristor is in parallel with the second path.

A fundamental frequency of the high voltage AC signal may be less than500 Hz, such as a frequency of substantially 60 Hz or substantially 50Hz for domestic mainsor a frequency of substantially 400 Hz for mains inships or aircraft. The high voltage capacitor may be of a value of nomore than 10 pF, 100 pF, 1 nF, 10 nF, 47 nF, 100 nF, 220 nF, 470 nF, 1μF, 4.7 μF or 10 μF. The high voltage capacitor may be an X or Y type orother capacitor. The high voltage capacitor may be formed from aparasitic. The high voltage capacitor may comprise plural, seriesconnected lower voltage capacitors. The high voltage AC signal may be atleast 100 Volts RMS, 200 Volts RMS, 300 Volts RMS or 400 Volts RMS. Thevoltage of the low voltage DC signal may be no more than half the peakvoltage of the high voltage AC signal. The low voltage DC signal may bearound 24 Volts, 15 Volts, 12 Volts, 5 Volts, 3.3 Volts, 2.5 Volts, 1.8Volts, 1.2 Volts or 0.9 Volts.

The power conversion apparatus may comprise a load circuit, such as aload comprising the like of communications circuitry, an SCR or a relayas described above. The load circuit may be comprised in a home controlnetwork. The load circuit may comprise an energy measurement arrangementsuch as by way of a shunt attached to live or neutral. The load circuitmay comprise a DIN meter, PANEL meter, Electronic meter or Home EnergyMonitor. The load circuit may comprise an electrical fault detectingcapability such as earth/ground fault, arc fault, residual currentdetection, overload protection or circuit breaker. The load circuit maybe low voltage switch gear. The load circuit may comprise a gas or smokedetector arrangement. The load circuit may comprise a presence orintruder alarm arrangement. The load circuit may be configured tocontrol a primary power supply of an appliance, information technologydevice, multimedia device or universal power supply. The load circuitmay be a secondary power supply that is used to control a primary powersupply when a device is in standby or power saving mode.

The power conversion apparatus described above may be used inapplications where there is more than one live phase in addition towhere there is live and neutral. According to a second aspect of thepresent invention there is therefore provided a power conversionarrangement comprising plural power conversion apparatus according tothe first aspect of the present invention.

According to a first approach, the power conversion arrangement may beconfigured such that the same high voltage capacitor is shared betweenthe plural power conversion apparatus and each power conversionapparatus is operative with a different one of plural phases. Adifferent load may therefore be supplied from each power conversionapparatus. By way of example according to this configuration one powerconversion apparatus may be coupled to a neutral phase conductor of ahigh voltage AC supply and the other power conversion apparatus may becoupled to a live phase conductor of the high voltage AC supply.

According to a second approach, the power conversion arrangement may beconfigured such that each of the plural power conversion apparatus isoperative with a different high voltage capacitor and the plural powerconversion apparatus are operative with the same phase. By way of anexample according to this configuration, one power conversion apparatusmay be coupled to a neutral phase of a high voltage AC supply with ahigh voltage capacitor coupled to one live phase, and another powerconversion apparatus may be coupled to the same neutral phase with ahigh voltage capacitor coupled to a different live phase.

According to a third approach, the plural power conversion apparatus maybe operative with the same phase and the power conversion arrangementmay be configured such that one of the power conversion apparatus isoperative to provide a positive voltage signal and another of the powerconversion apparatus is operative to provide a negative voltage signal.The power conversion arrangement may thus be configured to provide bothpositive and negative supply rails. The power conversion arrangement mayfurther comprise a rectifier arrangement disposed between each powerconversion apparatus and a shared high voltage capacitor. One of the tworectifier arrangements may be configured to provide for conductionduring a positive part of the waveform cycle and the other of the tworectifier arrangements may be configured to provide for conductionduring a negative part of the waveform cycle.

The power conversion arrangement may comprise a delta configuration ofthree pairs of power conversion apparatus in which each power conversionapparatus is coupled to a different phase of a three phase supply and inwhich adjacent power conversion apparatus of different pairs share thesame high voltage capacitor. The delta configuration may thereforecomprise three high voltage capacitors. Each of the three pairs of powerconversion apparatus may supply a different load. Each load maytherefore be supplied with power from two different phases. This mayprovide the advantage of redundancy whereby each load may be supplied byone phase in the event of failure of the other phase. In certain forms,the power conversion apparatus may be operative to carry current intheir first paths in both the positive and negative going parts of thecycle. Where the power conversion arrangement comprises a holdingcapacitor in each pair of power conversion apparatus, the holdingcapacitors may be smaller in size compared with configurations in whicha power conversion apparatus receives power from a single phase. Thismay provide the advantage of allowing for the use of a capacitortechnology that is ‘dry’ such as ceramic as opposed to ‘wet’ such aselectrolytic. Dry capacitor technology has more favourable lifetimereliability than wet capacitor technology. This is because the use ofthree phases may mean that there is, in effect, no dead period. Incertain applications, circumstances may be such that there is no needfor holding capacitors. The power conversion arrangement may thereforelack a holding capacitor.

The power conversion arrangement may comprise a star configurationcomprising at least three power conversion apparatus. Each of threepower conversion apparatus may be coupled to a respective high voltagecapacitor with each high voltage capacitor being coupled to a differentlive phase. The three power conversion apparatus may be coupled to theneutral phase. Each phase leg of the power conversion arrangement maycomprise a pair of power conversion apparatus in a back to backconfiguration with a high voltage capacitor therebetween. The delta andstar configurations may be combined in the same apparatus. The powerconversion arrangement may comprise, by way of another alternative, twolive phases and neutral in a split phase configuration. Each of the twolive phase legs of the power conversion arrangement may comprise a pairof power conversion apparatus in a back to back configuration with ahigh voltage capacitor therebetween. The split phase configuration mayfurther comprise a first power conversion apparatus coupled to a firstone of the two live phases and a high voltage capacitor and a secondpower conversion apparatus coupled to a second one of the two livephases and the high voltage capacitor.

Several different combinations of multi-phase configurations may beprovided in which the high voltage capacitor is shared and there is adifferent load and in which there are different high voltage capacitorsand a shared load. Such different combinations may be employed tomaximise benefits but at the expense of additional components. Forexample a multi phase and neutral arrangement may be configured tomaximise the power available with respect to neutral by providing pluralpower conversion apparatus in parallel on neutral with each powerconversion apparatus drawing current from a respective high voltagecapacitor relative to a respective phase. This approach may bebeneficial in respect of maximising the power on neutral, which canoften comprise additional electronics in a multi phase arrangement. Alsothis approach may afford a reduction in the requirement for a holdingcapacitor on account of the available power profile being the sum of theplural phases. By way of another example plural power conversionapparatus may share the high voltage capacitor relative to theirrespective phases whereby power may be provided to plural loads withoutan additional high voltage capacitor. By way of further example, thedelta and star configurations described above may be combined in thesame power conversion arrangement with or without a back to backconfiguration of power conversion apparatus for the star configuration.

The power conversion arrangement may be configured such that the pluralphases comprise at least one of: a single live phase and a neutralphase; two live phases and a neutral phase; two live phases with noneutral phase; three live phases and a neutral phase in a deltaconfiguration; three live phases with no neutral phase in a deltaconfiguration; three live phases and a neutral phase in a starconfiguration; three live phases with no neutral phase in a starconfiguration; and more than three live phases and a neutral phase.

Further embodiments of the second aspect of the present invention maycomprise one or more features of the first aspect of the presentinvention.

The present inventors have appreciated that the sharing of a holdingcapacitor between two power conversion apparatus is of widerapplicability than hitherto described. According to a third aspect ofthe present invention there is therefore provided a power conversionarrangement comprising plural power conversion apparatus, each powerconversion apparatus being configured to receive a high voltagealternating current signal at an input and to provide in dependencethereon a low voltage direct current signal from an output stage, thepower conversion apparatus comprising: a main path comprising a highvoltage capacitor in series with the input; a first path operative tocarry current carried by the main path one of a positive going part anda negative going part of the high voltage alternating current signal; asecond path operative to carry current carried by the main path in theother of a positive going part and a negative going part of the highvoltage alternating current signal; and first and second switches whichare operative to determine when a respective one of the first and secondpaths carries current, in which the high voltage capacitor is sharedbetween the plural power conversion apparatus and the first and secondswitches of at least one of the power conversion apparatus are operablein the absence of control signals.

The power conversion arrangement may be configured to be operative froma multi-phase supply as described above. The first and second switchesof at least one of the power conversion apparatus are operable in theabsence of control signals, such as control signals derived from the lowvoltage DC signal. The first and second switches may therefore beoperative of themselves and in dependence on the relative voltagesacross each switch. More specifically the first switch may be a diode.Alternatively or in addition the second switch may be a Zener diode.

Further features of the third aspect of the present invention maycomprise one or more further features of the first or second aspect ofthe present invention.

According to a further aspect of the present invention there is providedpower conversion apparatus configured to receive a high voltagealternating current signal at an input and to provide in dependencethereon a low voltage direct current signal from an output stage, thepower conversion apparatus comprising: a main path comprising a highvoltage capacitor in series with the input; a first path operative tocarry current carried by the main path in at least one of a positivegoing part and a negative going part of the high voltage alternatingcurrent signal; a second path operative to carry current carried by themain path in a positive going part and a negative going part of the highvoltage alternating current signal; and first and second switches whichare operative to determine when a respective one of the first and secondpaths carries current, the output stage receiving current flowing in thefirst path. Embodiments of the further aspect of the present maycomprise one or more features of any previous aspect of the presentinvention.

This summary is intended to provide an overview of subject matter of thepresent patent application. It is not intended to provide an exclusiveor exhaustive explanation of the invention. The detailed description isincluded to provide further information about the present patentapplication.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings, which are not necessarily drawn to scale, like numeralsmay describe similar components in different views. Like numerals havingdifferent letter suffixes may represent different instances of similarcomponents. The drawings illustrate generally, by way of example, butnot by way of limitation, various embodiments discussed in the presentdocument.

FIG. 1 is a circuit diagram of a capacitive transformerless powerconversion apparatus of known form;

FIG. 2 is a circuit diagram of a capacitive transformerless powerconversion apparatus according to a first embodiment of the presentinvention;

FIG. 3 is a circuit diagram of a capacitive tra.nsformerless powerconversion apparatus according to a second embodiment of the presentinvention;

FIG. 4A shows signal waveforms in the first embodiment in which theoutput voltage is elevated;

FIG. 4.B shows signal waveforms in the second embodiment in which theoutput voltage is elevated;

FIG. 5 is a circuit diagram of a capacitive transformerless powerconversion apparatus comprising a communications circuit;

FIG. 6A is a circuit diagram of a switch network comprised inembodiments of the present invention;

FIG. 6B is a circuit diagram of a first embodiment of a power conversionarrangement;

FIG. 6C is a circuit diagram of a second embodiment of a powerconversion arrangement;

FIG. 6D is a circuit diagram of a third embodiment of a power conversionarrangement; and

FIG. 6E shows signal waveforms in the third embodiment of FIG. 6D.

FIG. 7 illustrates generally an example of a power converter system thatcan include or use a capacitor.

FIG. 8 illustrates generally an example that includes a harvestingcapacitor coupled to a power converter system.

FIG. 9 illustrates generally an example that includes a PCB-basedharvesting capacitor coupled to a converter circuit.

DETAILED DESCRIPTION

A capacitive transformerless power conversion apparatus 40 according toa first embodiment of the present invention is shown in circuit diagramform in FIG. 2. The power conversion apparatus 40 comprises a liveconnection 42 and a neutral connection 44 which are connectedrespectively to the live and neutral conductors of a 240 V ACelectricity supply. A capacitor 46 (which constitutes a high voltagecapacitor), such as an X-type, Y-type, or other capacitor, and aresistor 48 are in series with the live connection 42 with a connectionbetween the capacitor 46 and the resistor 48 being represented byreference numeral 43. In certain forms, the high voltage capacitor isconstituted by plural series connected lower voltage capacitors. Theresistor 48 is present to limit the inrush current to the capacitor 46if the power conversion apparatus is connected to the mains at a pointin the mains cycle other than the zero crossing or in the event of amains surge. A discharge resistor 50 is connected across the capacitor46. The power conversion apparatus 40 further comprises a first switch52 in series with the capacitor 46 and the resistor 48. The powerconversion apparatus 40 also comprises a second switch 54 and a holdingcapacitor 56. The first terminal of the second switch 54 is electricallyconnected between the resistor 48 and the first terminal of the firstswitch 52 and the second terminal of the second switch 54 iselectrically connected to the neutral connection 44. Each of the firstand second switches 52, 54 is constituted by a pair of MOSFETs in a backto back configuration with a control input of the switch beingconstituted by the gates of the MOSFETs

The pair of MOSFETs is comprised in a well whose voltage bias is alteredduring operation to handle an increased voltage range. In an alternativeform each of the first and second switches 52, 54 is constituted by asingle MOSFET.

The single MOSFET is formed by an appropriate semiconductor process suchthat the MOSFET is capable of supporting the highest voltages present inthe power conversion apparatus 40. The power conversion apparatus 40also comprises a first protection device (not shown) in the form of aMOSFET acting as a cascade in series with the pair of MOSFETs and asecond protection device (not shown) in the form of a parasitic diode tothe substrate or well in parallel with the pair of MOSFETs. The holdingcapacitor 56 is electrically connected between the second terminal ofthe first switch 52 and the neutral connection 44.

The power conversion apparatus 40 yet further comprises an output stage.The output stage comprises a positive voltage output connection 58 atthe second terminal of the first switch 52 and a low voltage outputconnection 60 at the neutral side of the holding capacitor 56. The lowvoltage output connection 60 is directly electrically connected to theneutral connection 44. In other embodiments there is an electricalcomponent between the low voltage output connection 60 and the neutralconnection 44. In such other embodiments, for example, the resistor 48may be in the neutral leg instead of the live leg. Returning to thepresent embodiment, the capacitor 46 and the resistor 48 lie in a mainpath of the power conversion apparatus. The first switch 52 lies in afirst path of the power conversion apparatus and the second switch 54lies in a second path of the power conversion apparatus. The powerconversion apparatus 40 also comprises a switch control circuit 62 whichis powered from the output stage of the power conversion apparatus. Theswitch control circuit 62 is operative to generate control signals tocontrol, i.e. to close and open, the first and second switches 52,54.The switch control circuit 62 comprises a voltage divider arrangement64 comprising a first resistor 66, Ra, and a second resistor 68, Rb, inseries. The switch control circuit 62 also comprises an operationalamplifier 70, a voltage reference 72 and a digital control circuit 74.The inverting input of the operational amplifier 70 is electricallyconnected between the first and second resistors 66, 68 and thenon-inverting input of the operational amplifier 70 is electricallyconnected to the voltage reference 72. The digital control circuit 74,which generates control signals for the first and second switches 52,54, receives an input from the operational amplifier 70. The switchcontrol circuit 62 is operative to control the duty cycle of the firstand second switches 52, 54 to set the voltage at the output stage, Vout,to a desired level which is determined in accordance with the ratio ofthe first and second resistors 66, 68 and the value of the voltagereference 72,Vret, whereby Vout=Vref*(Ra+Rb)/Rb. Although not shown inFIG. 2, the switch control circuit 62 is further configured to determinewhen the first and second switches 52, 54 are opened and closed havingregard to the cycle of the mains supply to the power conversionapparatus 40. More specifically the switch control circuit 62 isconfigured to at least one of: measure a voltage across the first switch52; measure a voltage across the second switch 54; measure a voltageacross the input, e.g. between live and neutral; and measure a currentflowing through the second switch 54. The switch control circuit 62therefore further comprises appropriate voltage and current sensors.Measurement of the voltage across the input, i.e. between the liveconnection 42 and the neutral connection 44, provides for determinationof the zero-crossing point of the mains signal.

Operation of the first embodiment of the power conversion apparatus 40will now he described with reference to FIG. 2. The switch controlcircuit 62 is operative to determine when the mains supply is in apositive going part as indicated by the circled parts 75 in the waveform76 of FIG. 2. When the mains supply is in a positive going part, theswitch control circuit 62 is operative to generate control signals toclose the first switch 52 and open the second switch 54 if the latter isnot already open having regard to the duty cycle determined by theswitch control circuit 62. Normally and depending on load requirementsthe first switch 52 is opened and closed one time or several times whenthe mains supply is in the positive going part.

Upon closing of the first switch 52 current is conveyed by way of thefirst path to either charge the holding capacitor 56 or be drawn by aload connected to the output stage. Upon initial start-up of the powerconversion apparatus 40 and assuming little or no drain by a load, thefirst switch 52 is closed for most of the positive going part of themains cycle to provide a maximum rate of charging of the holdingcapacitor 56. As the holding capacitor 56 charges up the first switch 52is closed for less of the positive going part of the mains cycle. If theholding capacitor 56 is fully charged then the first switch 52 may notclose at all during one or more positive going parts of the mains cycle.On the other hand, if power demand from the load increases so as todrain the holding capacitor 56 the length of the closed time of thefirst switch 52 is increased during the positive going part of the mainscycle. The switch control circuit 62 also operative to close the secondswitch 54 when a clamping action is required, i.e. to limit an extent towhich the voltage at the first terminal of the first switch 52 excursestowards the live line voltage. The second switch 54 is therefore closedon an intermittent basis and primarily during the negative going part ofthe mains cycle when the power conversion apparatus is under load. Thesecond switch 54 also closes during the positive going part of the mainscycle at times when there is low load demand. The first switch 52 isopen when the second switch 54 is closed and vice-versa. The first andsecond switches 52, 54 are operated such that they are not closed at thesame time. More specifically the second switch 54 opens before the firstswitch closes 52 and the first switch 52 opens before the second switch54 closes. In certain forms, the first and second switches 52, 54 areclosed at the same time momentarily to reduce an extent of excursion ofvoltage on the capacitor 46. In an un-illustrated embodiment which is analternative to the embodiment shown in FIG. 2, a negative low voltage DCsupply is provided. In this alternative embodiment the capacitor 46 isin series with the low side of the input to the power conversionapparatus, i.e, the neutral connection 44. In addition the first andsecond switches 52, 54 are operative such that the holding capacitor 56is charged in the negative going part of the mains cycle. The outputfrom the power conversion apparatus is thus referenced to the live ofthe mains input.

In a further un-illustrated embodiment which is an alternative to theembodiment shown in FIG. 2, the power conversion apparatus furthercomprises a low voltage DC-DC converter, The low voltage DC-DC converteris connected between the holding capacitor 56 and the positive voltageoutput connection 58 and is configured to provide plural low voltage DCsupplies.

In a yet further un-illustrated embodiment which is an alternative tothe embodiment shown in FIG. 2, the power conversion apparatus furthercomprises a. switching converter. The switching converter is connectedbetween the holding capacitor 56 and the positive voltage outputconnection 58 and is configured to provide for increased current atreduced voltage from the power conversion apparatus.

A second embodiment of power conversion apparatus 90 will now bedescribed with reference to FIG. 3. Features of the second embodiment incommon with the first embodiment are indicated by common referencenumerals and the reader's attention is directed to the descriptionprovided above with reference to FIG. 2 for a description of such commonfeatures. Features particular to the second embodiment 90 will now bedescribed. The power conversion apparatus 90 comprises an intermediatecapacitor 92, a third switch 94, a fourth switch 96, a fifth switch 98and a sixth switch 100. In an alternative embodiment an intermediateinductor is used instead of the intermediate capacitor 92, Each of thethird to sixth switches 94. 96, 98, 100 is of the same form as the firstand second switches 52, 54. Although not shown in FIG. 3 the powerconversion apparatus 90 comprises a switch control circuit which isadapted to generate control signals to open and close each of the thirdto sixth switches 94, 96, 98, 100. The intermediate capacitor 92 isconnected in series between the first switch 52 and the output stage viaswitch 98. The third switch 94 is connected at a first end to a firstend of the intermediate capacitor 92, which is closer of the first andsecond ends of the intermediate capacitor 92 to the output stage, and ata second end to the neutral connection 44. The fourth switch 96 isconnected at a first end to the second end of the intermediate capacitor92 and at a second end to the neutral connection 44. The fifth switch 98is connected at a first end to the first end of the intermediatecapacitor 92 and at a second end to the positive voltage outputconnection 58 of the output stage. The sixth switch 100 is connected ata first end to the second end of the intermediate capacitor 92 and at asecond end to the positive voltage output connection 58 of the outputstage.

Operation of the second embodiment of power conversion apparatus 90 willnow be described with reference to FIG. 3. The second embodiment ofpower conversion apparatus 90 is operative to provide for charging ofthe holding capacitor 56 in dependence on current flow during both ofthe positive and negative going parts of the mains cycle. This incontrast with the first embodiment of power conversion apparatus 40which is operative to provide for charging of the holding capacitor 56in dependence on current flow during the positive going part only.During the negative going part of the mains cycle as determined by theswitch control circuit, the switch control circuit is operative togenerate control signals which close the first and third switches 52, 94during a first phase and which close the fourth and fifth switches 96,98 during a second phase. During each of the first and second phases allother switches are open. The switch control circuit is operative tochange between the first and second phases at a frequency between 100kHz and 100 MHz. Charge flows into the intermediate capacitor 92 duringthe first phase. Charge then flows from the intermediate capacitor 92 tothe holding capacitor 56 during the second phase. During the positivegoing part of the mains cycle as determined by the switch controlcircuit, the switch control circuit is operative to generate controlsignals which close the first and fifth switches 52, 98 during a thirdphase and which close the third and sixth switches 94, 100 during afourth phase. During each of the third and fourth phases all otherswitches are open. The switch control circuit is operative to changebetween the third and fourth phases at a frequency between 100 kHz and100 MHz. Charge flows into the intermediate capacitor 92 and the holdingcapacitor 56 during the third phase. Charge then flows from theintermediate capacitor 92 to the holding capacitor 56 during the fourthphase. The present approach therefore provides for twice the chargeduring the positive going part compared with the first embodiment.Otherwise the second embodiment of power conversion apparatus 90 isoperative in the same fashion as the first embodiment of powerconversion apparatus 40. For example the switch control circuit isoperative to change the duty cycle of switching from one of the first tofourth phases to the second switch 54 to maintain the voltage at theoutput stage at a desired level. Also the switch control circuit isoperative to close the second switch 54 to limit an extent to which thevoltage at the first terminal of the first switch 52 excurses towardsthe live line voltage.

In the embodiment of FIG. 3 the first and third to sixth switches andthe intermediate capacitor constitute a first path arrangement. Inalternative, un-illustrated embodiments to the embodiment of FIG. 3 thepower conversion apparatus comprises plural such first patharrangements. in one form the plural first path arrangements charge thesame holding capacitor 56. Having plural such first path arrangementsprovides for smoother transfer of power to the holding capacitor. Inanother form each of the plural first path arrangements charges adifferent holding capacitor. In addition the switches of the first patharrangements are operative to provide for either different voltagelevels of DC output or for a mix of positive and negative voltage DCoutputs. The power conversion apparatus may therefore be configured toprovide a differential power supply.

In an un-illustrated alternative embodiment to the embodiment shown inFIG. 3 the intermediate capacitor is replace with an intermediateinductor. The form of the first to sixth switches is unchanged with theexception of the sixth switch 100 being identified as the fourth switchand the fourth switch 96 being identified as the sixth switch. Operationof the embodiment comprising the intermediate inductor is the along thesame lines as operation of the embodiment comprising the intermediateconductor having regard to the different identities of the fourth andsixth switches.

Considering the operation in more detail, during the negative going partof the mains cycle as determined by the switch control circuit, theswitch control circuit is operative to generate control signals whichclose the first and third switches 52, 94 during a first phase and whichclose the third and fourth switches 94, 100 during a second phase.During each of the first and second phases all other switches are open.Energy flows into the intermediate inductor during the first phase.Energy then flows from the intermediate inductor to the holdingcapacitor during the second phase. During the positive going part of themains cycle as determined by the switch control circuit, the switchcontrol circuit is operative to generate control signals which close thefirst and fifth switches 52, 98 during a third phase and which close thefifth and sixth switches 98, 96 during a fourth phase. During each ofthe third and fourth phases all other switches are open. Energy flowsinto the intermediate inductor and the holding capacitor 56 during thethird phase. Energy then flows from the intermediate inductor to theholding capacitor 56 during the fourth phase. Otherwise operation of theembodiment comprising the intermediate inductor is the same as operationof the embodiment comprising the intermediate capacitor.

With regard to the provision of plural first path arrangements in theembodiment comprising the intermediate inductor, in a first form eachfirst path arrangement comprises a different intermediate inductor anddifferent first and third to sixth switches. According to one approachthe plural first path arrangements charge the same holding capacitor 56.According to another approach the plural first path arrangements chargedifferent holding capacitors 56 to thereby provide either differentvoltage levels of DC output or a mix of positive and negative voltage DCoutputs. In a second form, each first path arrangement comprises adifferent intermediate inductor and different fourth and fifth switcheswith the first, third and sixth switches being common to the pluralfirst path arrangements. In the second form each first path arrangementfurther comprises a different holding capacitor whereby the second formis operative to provide plural DC outputs.

Signal waveforms in the first embodiment are shown in FIG. 4A. The upperwaveform 102 represents the mains signal and the lower waveform 104represents the signal at the output stage from the power conversionapparatus 40. The upper waveform 102 has portions, namely dead periods106, where there is no charging of the power conversion apparatus. Thedead periods 106 are during the nearly flat and negative going parts ofthe mains signal when there is no charging of the holding capacitor 56.Charge lost from the holding capacitor 56 on account of load draw andleakage is not replenished the dead periods 106. The switch controlcircuit 62 is therefore operative to over-charge the holding capacitor56 just before the start of a dead period such that the voltage at theoutput stage is higher 108 than the desired level to thereby compensatefor lower charge availability during the following dead period 116.

Signal waveforms in the second embodiment are shown in FIG. 48. Theupper waveform 112 represents the mains signal and the lower waveform114 represents the signal at the output stage from the power conversionapparatus 90, The upper waveform 112 has portions, namely dead periods116, where there is little or no charging of the power conversionapparatus. The dead periods are around the maximum and minimum points ofthe mains signal when the rate of change of the signal is low. Chargelost from the holding capacitor 56 on account of load draw and leakageis replenished at a slower rate during the dead periods. The switchcontrol circuit 62 is therefore operative to over-charge the holdingcapacitor 56 just before the start of a dead period such that thevoltage at the output stage is higher 118 than the desired level tothereby compensate for lower charge availability during the followingdead period 116.

In un-illustrated forms of the first and second embodiments, the switchcontrol circuit 62 is adapted to monitor the mains signal and to analysethe mains signal to determine its condition or to detect a faultcondition, such as a brownout or loss of a single phase. The switchcontrol circuit 62 is adapted to generate control data which is conveyedto a load connected to the power conversion apparatus 40, 90. Thecontrol data is configured such that the load is controlled to takeaction appropriate to a detected fault condition or a determinedcondition of the mains cycle. The control data may, for example, beconfigured to cause the load to enter a low power consumption state whena fault is detected. By way of another example, the control data may beconfigured to cause the load to increase its demand during parts of themains cycle between the dead period and to decrease its demand duringdead periods. In further un-illustrated forms of the first and secondembodiments, the switch control circuit 62 is adapted to receive controldata from a load and to control operation of the power conversionapparatus in dependence on the received control data. For example andwhere the load is about to enter a low power state, the control data isconfigured to cause the power conversion apparatus to delay releasingthe capacitor 46 from the neutral connection 44. By way of anotherexample and where the load is about to draw an increased level of power,the control data is configured to cause the power conversion apparatusto increase the level of charge on the holding capacitor 56.

A capacitive transformerless power conversion apparatus 130 comprising acommunications circuit is shown in circuit diagram form in FIG. 5.Features of the circuit of FIG. 5 in common with the first embodiment ofFIG. 2 are indicated with common reference numerals and the reader'sattention is directed to the description provided above with referenceto FIG. 2 for a description of such common features. Features particularto the circuit 130 of FIG. 5 will now be described. It will be readilyappreciated by the reader skilled in the art that the second embodimentof FIG. 3 may be re-configured without exercising any more than ordinarydesign skill such that it comprises the communications circuit of FIG.5. The power conversion apparatus 130 of FIG. 5 comprises acommunications circuit 132, which is operable to receive and transmitdata at a communications circuit port, and a seventh switch 134. Theseventh switch 134 is of the same form as the first and second switches52, 54. The first terminal of the seventh switch 134 is electricallyconnected to the communications circuit port and the second terminal ofthe seventh switch 134 is electrically connected to the first terminalof the first switch 52 such that the second terminal of the seventhswitch 134 connects between the first switch 52 and the resistor 48. Thecommunications circuit 132 draws power from the output stage of thepower conversion apparatus. Operation of the power conversion apparatus130 of FIG. 5 will now be described. Prior to the reception of data byor transmission of data from the communications circuit 132, the switchcontrol circuit is operative to close the seventh switch 134 and to openall other switches in the power conversion apparatus 136. Thecommunications circuit 132 is then operative to generate communicationdata at its communications circuit port which is conveyed by way of theresistor 48 and the capacitor 46 to the mains supply for onwardtransmission to the like of a supervisory and control circuit.Alternatively communication data is received from the mains supply andis conveyed by way of the capacitor 46, the resistor 48 and the seventhswitch 134 to the communications circuit port of the communicationscircuit 132. At other times 138, i.e. when there is no communication ofdata to or from the communications circuit 132, the seventh switch 134is open and the other switches in the power conversion apparatus 130 areoperative as described above with reference to FIG. 2.

First to third embodiments of a power conversion arrangement will now bedescribed with reference to FIGS. 6A to 6E. A circuit diagram of aswitch network 140 comprised in the first to third embodiments of thepower conversion arrangement is shown in FIG. 6A. Features of the switchnetwork 140 of FIG. 6A in common with the second embodiment of FIG. 3are indicated with common reference numerals and the reader's attentionis directed to the description provided above with reference to FIG. 3for a description of such common features. Features particular to theswitch network 140 of FIG. 6A will now be described. As can be seen fromFIG. 6A, the switch network 140 lacks the capacitor 46 and the holdingcapacitor 56. The live connection to the switch network 140 of FIG. 6Ais therefore constituted by node 43. Furthermore the switch network 140is equivalent to the circuit block 142 shown towards the lower part ofFIG. 6A.

A first embodiment of a power conversion arrangement 150 is shown inFIG. 68. The power conversion arrangement 150 comprises two switchnetworks 142, with one switch network 142 being coupled at a low circuitside to the live conductor of a mains supply and the other switchnetwork 142 being coupled at a low circuit side to the neutral conductorof a mains supply. Each of the switch networks 142 has a holdingcapacitor 152 connected across its output stage and a different load 154connected to its output stage. In addition a first terminal of an X typecapacitor 156 is connected to the high side of the switch network 142that is coupled at its low circuit side to the neutral conductor of themains supply. A second terminal of the X type capacitor 156 is connectedto the high side of the switch network 142. that is coupled at its lowcircuit side to the live conductor of the mains supply. The X typecapacitor 156 is therefore shared between the two switch networks 142.Otherwise each switch network 142 has a form and function as describedabove with reference to either FIG. 2 or FIG. 3.

A circuit diagram of a second embodiment of a power conversionarrangement 160 is shown in FIG. 6C. Features of the second embodimentof power conversion arrangement 160 in common with the first embodimentof power conversion arrangement 150 are indicated with common referencenumerals and the reader's attention is directed to the descriptionprovided above with reference to FIG. 68 for a description of suchcommon features. Features particular to the second embodiment of powerconversion arrangement 160 will now be described. The second embodimentcomprises a diode 162 and a Zener diode 164 instead of each switchnetwork 142 in the same configuration as shown in FIG. 1. The switchesof the second embodiment are therefore operative of themselves, i.e; independence on the relative voltage levels of the diodes 162 and Zenerdiodes 164, instead of in dependence on control signals. The secondembodiment of power conversion arrangement 160 therefore lacks theswitch control circuits of previous embodiments. Otherwise the secondembodiment of power conversion arrangement 160 operates in the samefashion as the first embodiment of power conversion arrangement 150 withthe X type capacitor 156 being shared.

A circuit diagram of a third embodiment of a power conversionarrangement 170 is shown in FIG. 6D, The third embodiment of powerconversion arrangement 170 comprises three pairs of power conversionapparatus in a delta configuration. Each pair of power conversionapparatus comprises two switch networks 142, which provide power to adifferent one of three loads 172, and a holding capacitor 174. Each pairof power conversion apparatus is coupled at its low input side to adifferent phase of a three phase mains supply. The high input side ofeach switch network 142 in each pair is electrically connected to adifferent terminal of an X type capacitor 176 and such each of threedifferent X type capacitors 176 is shared between adjacent pairs ofpower conversion apparatus in the delta configuration. More specificallyeach pair of power conversion apparatus is electrically coupled at eachof its two high input sides with its neighbouring pair of powerconversion apparatus with an X type capacitor 176 being in seriesbetween each neighbouring pair of power conversion apparatus. The switchnetworks 142 and power conversion apparatus comprised in the thirdembodiment of power conversion arrangement 170 are of a form andfunction as described above with reference to FIG. 3. Signal waveforms180 of the third embodiment of FIG. 6D are shown in FIG. 6E. The topplot 182 shows the voltage waveform of three phases of the mains supply.The middle plot 184 shows the delta-voltage waveforms for the pair ofpower conversion apparatus coupled to a first phase. As can be seen fromthe middle plot, there is power available during the circled parts 185of the waveforms and therefore power available substantially all of thetime on account of the phase relationship of the three phase supply. Thebottom plot 186 shows the available power on they axis against time onthe x axis with two of three single phase waveforms 188 represented andthe combination of the two single phase waveforms 190 also represented.As can be appreciated from the bottom plot 186, there are substantiallyno dead periods 192 and the peak power of the combination of the threesingle phase waveforms 190 is substantially higher compared with thesingle phase waveforms 188.

In an un-illustrated embodiment the power conversion arrangement has astar configuration having first to third power conversion apparatus.Each of the first to third power conversion apparatus is coupled to arespective high voltage capacitor with each of the three high voltagecapacitors being coupled to a different live phase. The three powerconversion apparatus are coupled to the neutral phase. In a form of thepresent embodiment, the star configuration further comprises threefurther power conversion apparatus and is configured such that eachphase leg of the power conversion arrangement comprises a pair of powerconversion apparatus in a back to back configuration with the highvoltage capacitor therebetween. This back to back configuration of powerconversion apparatus and high voltage capacitor is as is shown in eachof the three legs of the delta configuration of FIG. 6D. According toanother embodiment the present star configuration and the abovedescribed delta configuration are combined in the same apparatus. Thecombining of the star and delta configurations in the same apparatuswill be within the ordinary design skills of the person skilled in theart. In another un-illustrated embodiment the power conversionarrangement comprises two live phases and neutral in a split phaseconfiguration with each of the two live phase legs of the powerconversion arrangement comprising a pair of power conversion apparatusin a back to back configuration with a high voltage capacitor. The splitphase configuration further comprises a first power conversion apparatuscoupled to a first one of the two live phases and a further high voltagecapacitor and a second power conversion apparatus coupled to a secondone of the two live phases and the same further high voltage capacitor.

In a further un-illustrated embodiment the power conversion arrangementcomprises first and second power conversion apparatus which are coupledto the same phase, such as the same live phase. The first and secondpower conversion apparatus share the same high voltage capacitor. Arectifier, such as a diode, is disposed between each of the first andsecond power conversion apparatus and the high voltage capacitor suchthat the two rectifiers are of opposite polarity. In use, the firstpower conversion apparatus is configured to transfer power to its loadin a positive going part only of the high voltage AC signal and thesecond power conversion apparatus is configured to transfer power to itsload in a negative going part only of the high voltage AC signal.

A portion of a power converter can be configured for electric fieldenergy harvesting or energy scavenging using a capacitive coupling. Inan example, one or more of the power converter examples discussed hereincan include or use a capacitor, such as the capacitor 46. The capacitor46 can be configured to harvest or convert energy from a source, such asfrom the live connection 42, for storage or use in powering anotherdevice.

FIG. 7 illustrates generally an example of a power converter system thatcan include or use a capacitor 746. The capacitor 746 can have variousforms but is generally configured to harvest energy from an electricfield, such as from a power transmission line. In an example, thecapacitor 746 is substituted for, or used together with, the highvoltage capacitor 46 (C1) described in the examples of FIGS. 2, 3, and5, among others.

In an example, the capacitor 746 is configured to harvest energy from atransmission line and provide a first power signal to a first convertercircuit 741. The first converter circuit 741 can include variouscomponents from the converter circuits described herein in the exampleso FIGS. 2, 3, and 5. For example, with reference to the example of FIG.2, the first converter circuit 741 can include one or more of theresistor 48 and the first and second switches 52 and 54. In an example,the first converter circuit 741 further includes the switch controlcircuit 62. In some examples, a resistor is not used between thecapacitor 746 and the first and second switches 52 and 54.

Following the first converter circuit 741, the example of FIG. 7includes a first energy storage circuit 756. The first energy storagecircuit 756 is configured to store a portion of the energy harvestedusing the capacitor 746. In an example, the first energy storage circuit756 corresponds to or includes the holding capacitor 56 from theexamples of FIG. 2, 3, or 5.

In the example of FIG. 7, an output of the first converter circuit 741and/or the first energy storage circuit 756 can be coupled to a secondconverter circuit 742. The second converter circuit 742 can be a DC-DCconverter circuit, such as configured to increase or decrease amagnitude of a received voltage signal. The second converter circuit 742can include a buck converter to decrease a magnitude of a voltage signalreceived from the first converter circuit 741, or a boost converter toincrease a magnitude of the voltage signal received from the firstconverter circuit 741, among other types of converters. In an example,the second converter circuit 742. is configured to down-convert areceived signal to about 5 to 20 volts.

A second energy storage circuit 757 can be coupled to an output of thesecond converter circuit 742, such as to store a voltage signal at ahigher or lower signal level than is stored by the first energy storagecircuit 756. Outputs from one or both of the second converter circuit742 and the second energy storage circuit 757 can be coupled to a firstload circuit 701. In an example, the first load circuit 701 comprises asensor or other device or module that can be used or power cycled atvarious times. For example, the first load circuit 701 can include anenvironmental sensor, such as powered using the converted energyharvested using the capacitor 746, and the environmental sensor can beconfigured to periodically monitor or sample one or more environmentalconditions such as temperature or humidity. Other types of sensors ordevices can similarly be used.

In an example, an electric field energy harvesting circuit or systemincludes or uses a pair of conductors that are spaced apart by adielectric or insulator member. In an example, a first conductor can bea portion of a power transmission line, such as for a mains or other ACsignal. A second conductor can be provided around the first conductorand spaced apart from the first conductor using the dielectric. Usedtogether, the first and second conductors comprise portions of acapacitor, such as the capacitor 746 from the example of FIG. 7. Inother words, the energy harvesting example can include a conductivesheath or cylinder that can be used as part of a capacitor to extractenergy from an electric field, such as an electric field about atransmission line that carries an electrical signal. In an example, theconductive cylinder can be formed from multiple conductive components orpieces that are electrically connected around an existing transmissionline. For example, the conductive sheath can be comprised of conductivetape, foil, or other material that can placed about a transmission linewithout disconnecting the transmission line and threading it through aunitary cylinder. Thus the present energy harvesting system can beapplied to an existing transmission line without interrupting a serviceprovided by such line.

FIG. 8 illustrates generally an example that includes a harvestingcapacitor 846 coupled to a power converter system 840, The harvestingcapacitor 846 includes a conductive sheath that surrounds a portion of afirst transmission line 810. The first transmission line is configuredto carry an AC signal, such as up to and including an AC signal having akilovolt swing or more. The first transmission line 810 includes asingle phase conductor, however, multiple phase conductors can be used.In an example, the converter circuit 840 includes the power conversionapparatus 40, and the harvesting capacitor 846 includes the high voltagecapacitor C1 from the examples of FIGS. 2, 3, and 5, among others.

The example of FIG. 8 can similarly be applied across multiple differentphases in a multiple-phase power distribution system, For instance,respective different harvesting capacitors (e.g., cylindrical sheathcapacitors or other style capacitors) can be provided around differenttransmission lines carrying different phase signals. In an example, acommon harvesting capacitor (e.g., a cylindrical sheath capacitor orother style capacitor) can be provided around multiple discretetransmission lines that carry different phase signals.

In an example, an energy harvesting system includes a conductivecylinder provided about, but spaced apart from, an inner conductor, Sucha system can be modeled by a pair of capacitors connected in series. Afirst capacitor represents a capacitance between the inner conductor andthe conductive cylinder, and a second capacitor represents a capacitancebetween the conductive cylinder and a reference (e.g., earth ground).Another device, such as an active sensor, or power storage device orbattery, can be coupled as a resistive load that is coupled in parallelwith the first capacitor, for example, the first load circuit 701 fromthe example of FIG. 7.

In an example, an energy harvesting system includes a capacitor formedby parallel pads on different layers of a circuit board. For example, amains or other source signal can be coupled to a first pad on a firstlayer of the circuit board. The first pad provides a first conductor ofa harvesting capacitor. A second pad on a different second layer of thecircuit can provide a second conductor of the harvesting capacitor. Inan example, each of the pads has a surface area of about one squarecentimeter separated by a layer of FR-4 epoxy. Such a configurationprovides a capacitor of around 7 pF. When the example capacitor isdriven by a 230V RMS signal (e.g., at 50 Hz), the capacitor yields about400 nA and the output voltage can be converted to about 20 V. The outputcan provide about 8 uW of power.

FIG. 9 illustrates generally an example that includes a PCB-basedharvesting capacitor coupled to a converter circuit. In the example, afirst multiple-layer PCB 910 includes a first pad 901 on a first layerand a second pad 902 on a different second layer. The layers can bespaced apart using a dielectric layer FR-4 or other insulator). In theexample, the first pad 901 is coupled to the first transmission line810, such as can include a conductor that carries one of multiple phasesin a power distribution system. When the first pad 901 is energized by asignal from the first transmission line 810, a first capacitance C1exists between the first and second pads 901 and 902. A secondcapacitance C2 can exist between the PCB 910 and ground 920. An electricfield harvested by C1 can be provided to the convert circuit 840 asshown.

A harvested power signal from an electric field energy harvesting systemcan be stored or used to power a device. In an example, a harvestedpower signal is used to power a sensor device or a transceiver, such asfor use in an Internet of Things environment. In an example, theharvested power signal is used to power one or more of an environmentalsensor configured to monitor or record information about temperature orhumidity; a motion sensor such as a tilt sensor, vibration sensor,accelerometer, or gyroscope configured to monitor position changes; asleep/wake circuit that is configured to periodically trigger activityby another circuit or sensor; a timer circuit; an MD or other datacommunication circuit; a tracking device; a WiFi-enabled sensor; anoptical sensor; a data recorder; a mechanical stress sensor; an acousticsensor; a utility consumption sensor; or other device or processor.

Various Notes

The above description includes references to the accompanying drawings,which form a part of the detailed description. The drawings show, by wayof illustration, specific embodiments in which the invention can bepracticed. These embodiments are also referred to herein as “examples.”Such examples can include elements in addition to those shown ordescribed, However, the present inventors also contemplate examples inwhich only those elements shown or described are provided. Moreover, thepresent inventors also contemplate examples using any combination orpermutation of those elements shown or described (or one or more aspectsthereof), either with respect to a particular example (or one or moreaspects thereof), or with respect to other examples (or one or moreaspects thereof) shown or described herein.

In the event of inconsistent usages between this document and anydocuments so incorporated by reference, the usage in this documentcontrols.

In this document, the terms “a” or “an” are used, as is common in patentdocuments, to include one or more than one, independent of any otherinstances or usages of “at least one” or “one or more.” In thisdocument, the term “or” is used to refer to a nonexclusive or, such that“A or B” includes “A but not B,” “13 but not A,” and “A and B,” unlessotherwise indicated. In this document, the terms “including” and “inwhich” are used as the plain-English equivalents of the respective terms“comprising” and “wherein.” Also, in the following claims, the terms“including” and “comprising” are open-ended, that is, a system, device,article, composition, formulation, or process that includes elements inaddition to those listed after such a term in a claim are still deemedto fall within the scope of that claim. Moreover, in the followingclaims, the terms “first,” “second,” and “third,” etc. are used merelyas labels, and are not intended to impose numerical requirements ontheir objects.

Geometric terms, such as “parallel”, “perpendicular”, “round”, or“square”, are not intended to require absolute mathematical precision,unless the context indicates otherwise. Instead, such geometric termsallow for variations due to manufacturing or equivalent functions. Forexample, if an element is described as “round” or “generally round,” acomponent that is not precisely circular (e.g., one that is slightlyoblong or is a many-sided polygon) still encompassed by thisdescription.

Method examples described herein can be machine or computer-implementedat least in part. Some examples can include a computer-readable mediumor machine-readable medium encoded with instructions operable toconfigure an electronic device to perform methods as described in theabove examples. An implementation of such methods can include code, suchas microcode, assembly language code, a higher-level language code, orthe like. Such code can include computer readable instructions forperforming various methods. The code may form portions of computerprogram products. Further, in an example, the code can be tangiblystored on one or more volatile, non-transitory, or non-volatile tangiblecomputer-readable media, such as during execution or at other times.Examples of these tangible computer-readable media can include, but arenot limited to, hard disks, removable magnetic disks, removable opticaldisks (e.g., compact disks and digital video disks), magnetic cassettes,memory cards or sticks, random access memories (RAMs), read onlymemories (ROMs), and the like.

The above description is intended to be illustrative, and notrestrictive. For example, the above-described examples (or one or moreaspects thereof) may be used in combination with each other. Otherembodiments can be used, such as by one of ordinary skill in the artupon reviewing the above description. The Abstract is provided to complywith 37 C.F.R. § 1.72(b), to allow the reader to quickly ascertain thenature of the technical disclosure. It is submitted with theunderstanding that it will not be used to interpret or limit the scopeor meaning of the claims. Also, in the above Detailed Description,various features may be grouped together to streamline the disclosure.This should not be interpreted as intending that an unclaimed disclosedfeature is essential to any claim. Rather, inventive subject matter maylie in less than all features of a particular disclosed embodiment.Thus, the following claims are hereby incorporated into the DetailedDescription as examples or embodiments, with each claim standing on itsown as a separate embodiment, and it is contemplated that suchembodiments can be combined with each other in various combinations orpermutations. The scope of the invention should be determined withreference to the appended claims, along with the full scope ofequivalents to which such claims are entitled.

The claimed invention is:
 1. A power conversion system configured toreceive a high voltage alternating current (AC) signal at an input stageof the system and to provide, based on the high voltage AC signal, a lowvoltage direct current (DC) signal from an output stage of the system,the power conversion system comprising: a first capacitor comprisingfirst and second conductors, wherein the first conductor comprises aportion of a main path for the high voltage AC signal; a first pathconfigured to carry current from the first capacitor in at least one ofa positive going part and a negative going part of the high voltage ACsignal; and a second path configured to selectively shunt current fromthe first capacitor in one or both of the positive going part and thenegative going part of the high voltage AC signal; wherein the outputstage receives current flowing in the first path.
 2. The powerconversion system of claim 1, further comprising a dielectric materialprovided about the first conductor, and wherein the second conductor ofthe first capacitor comprises a conductive member that surrounds aportion of the dielectric material and the first conductor along a firstlength of the first conductor.
 3. The power conversion system of claim2, wherein the first conductor comprises a transmission line for a powermains signal.
 4. The power conversion system of claim 1, wherein thefirst and second conductors of the first capacitor include respectivepads on parallel layers of a circuit board.
 5. The power conversionsystem of claim 1, further comprising first and second switchesconfigured to control current flow to the first and second paths,respectively.
 6. The power conversion system of claim 5, wherein atleast one of the first and second switches operates based on a controlsignal, and wherein the control signal is based on the low voltage DCsignal from the output stage.
 7. The power conversion system of claim 5,wherein the first and second switches are operative substantially out ofphase with each other.
 8. The power conversion system of claim 5,wherein at least one of the first and second switches is switched at afrequency greater than a frequency of the high voltage AC signal.
 9. Thepower conversion system of claim 5, wherein the first path is configuredto carry current in both the positive going part and the negative goingpart of the high voltage AC signal, the power conversion systemcomprising an intermediate energy storing component and third, fourthand fifth switches which are each operable in dependence on a controlsignal derived from the low voltage direct current signal, and whereinthe intermediate energy storing component comprises one of anintermediate capacitor and an intermediate inductor, the intermediateenergy storing component being disposed in series between the firstcapacitor and the output stage.
 10. The power conversion system of claim1, wherein the first path is in series with the output stage and thesecond path is in parallel with the output stage.
 11. The powerconversion system of claim 1, wherein each of the first and second pathsis configured to carry current in less than all of the positive goingpart or the negative going part within a cycle of the high voltage ACsignal.
 12. The power conversion system of claim 1, further comprising aDC-DC converter circuit configured to receive a first output signalhaving a first voltage magnitude from the output stage and provide asecond output signal having a lesser second voltage magnitude.
 13. Amethod for providing a low voltage direct current (DC) signal from anoutput stage of a power conversion system based on a received highvoltage alternating current (AC) signal at an input stage of the system,the system including a main path with a capacitor in series with theinput, the method comprising: in a first path, carrying current from themain path in at least one of a positive going part and a negative goingpart of the high voltage AC signal; in a second path, shunting currentfrom the main path in a positive going part and a negative going part ofthe high voltage AC signal; controlling first and second switchesrespectively disposed in the first and second paths to modulate currentflowing from the main path to the first and second paths; and receiving,at the output stage, an output signal from the first path.
 14. Themethod of claim 13, wherein the controlling the first and secondswitches includes controlling the switches using a control signal thatis based on the low voltage DC signal.
 15. The method of claim 13,further comprising receiving a current in the main path from an AC mainssignal using the capacitor that is in series with the input, thecapacitor including a conductor provided around a portion of atransmission line carrying the AC mains signal and configured to harvestenergy from an electric field produced by the AC mains signal.
 16. Themethod of claim 13, wherein the controlling the first and secondswitches includes operating the switches substantially out of phase witheach other and switching at least one of the first and second switchesat a frequency that is greater than a frequency of the high voltage ACsignal.
 17. The method of claim 13, further comprising receiving theoutput signal and down-converting an amplitude of the output signalusing a DC-DC converter circuit.
 18. An energy harvesting and powerconversion system configured to receive a high voltage alternatingcurrent (AC) signal at an input stage of the system and to provide,based on the high voltage AC signal, a low voltage direct current (DC)signal from an output stage of the system, the power conversion systemcomprising: an electric field energy harvesting circuit comprising aportion of a main path for the high voltage AC signal; a first pathconfigured to carry current from the harvesting circuit in at least oneof a positive going part and a negative going part of the high voltageAC signal; and a second path configured to carry current from theharvesting circuit in the positive going part and negative going part ofthe high voltage AC signal; wherein the output stage receives currentflowing in the first path.
 19. The energy harvesting and powerconversion system of claim 18, wherein the electric field energyharvesting circuit comprises a first capacitor with first and secondconductors, wherein the first conductor comprises the portion of themain path for the high voltage AC signal.
 20. The energy harvesting andpower conversion system of claim 19, wherein the second conductor of thefirst capacitor comprises a cylindrical conductor that is spaced apartfrom and provided coaxially with the first conductor of the firstcapacitor.
 21. The energy harvesting and power conversion system ofclaim 19, wherein the first and second conductors of the first capacitorcomprise pads of a circuit board provided on respective parallel andspaced apart layers of the circuit board.
 22. The power conversionsystem of claim 18, further comprising first and second switchesconfigured to control current flow to the first and second paths,respectively.
 23. The power conversion system of claim 22, wherein atleast one of the first and second switches operates based on a controlsignal, and wherein the control signal is based on the low voltage DCsignal from the output stage.